The peripheral nervous system (PNS) serves as a bridge between the environment and the central nervous system (CNS). The PNS is comprised of primary afferent neurons, which sends information from sensory receptors to the CNS, somatic motor neurons, which transmit electrical stimuli from the CNS to voluntary muscles, and autonomic motor neurons, which transmit electrical stimuli to cardiac muscle, smooth muscle or glands. A neuron generally has a cell body, and an axon, which is a long nerve cell process extending from the cell body that is capable of rapidly conducting nerve impulses over long distances so as to deliver signals to cells. The axons of many vertebrate neurons are insulated by a myelin sheath, which greatly increases the rate at which an axon can conduct an action potential. Schwann cells are responsible for myelinating nerve cells in the peripheral nervous system. The Schwann cells wrap layer upon layer of their own plasma membrane in a tight spiral around the axon thereby insulating the axonal membrane so that almost no current leaks across it. Unmyelinated axons in the PNS are nonetheless embedded in Schwann cells although they are not ensheathed by myelin.
A number of neuropathies of the PNS are associated with demyelination or failure of the Schwann cells to properly ensheath the axons of the PNS. They are diabetic neuropathy, Guillain-Barrxc3xa9 disease (acute demyelinating polyneuropathy), chronic inflammatory demyelinating polyradiculoneuropathy (CIPD), and HIV inflammatory demyelinating disease. Also axon damage due to physical trauma may result in demyelination of the PNS. Thus, there is a need to discover agents that can be used to promote the production of myelin by Schwann cells.
The present invention fills this need by providing for a method for promoting production of myelin or P zero protein by Schwann cell comprising bringing a Zcyto7 polypeptide or IL-17 into contact with Schwann cells. Examples of Zcyto7 polypeptides are the polypeptides of SEQ ID NOs: 2, 7, and 9-28.
Preferably, the mammal treated will be a human and the Zcyto7 will be of the human allotypes. Preferably, the Zcyto7 will be administered in an amount of about 0.1 to 100 micrograms (xcexcg) per kilogram of body weight.
The teachings of all of the references cited in the present specification are incorporated in their entirety herein by reference.
Definitions
The term xe2x80x9ceffective amountxe2x80x9d as used herein regarding the effective amount of Zcyto7 administered in accordance with the present invention means an amount of Zcyto7 that causes increased expression of myelin by Schwann cells. The effective amount of Zcyto7 or IL-17 to be administered is from 0.1 xcexcg to 1 mg of Zcyto7 or IL-17 per kilogram of body weight per day. More preferably, the effective amount is from 1 xcexcg to 500 xcexcg of Zcyto7 or IL-17 per kilogram of body weight. Zcyto7 should be administered daily until the symptoms of neuropathy dissipate.
The term xe2x80x9callelic variantxe2x80x9d denotes any of two or more alternative forms of a gene occupying the same chromosomal locus. Allelic variation arises naturally through mutation, and may result in phenotypic polymorphism within populations. Gene mutations can be silent (no change in the encoded polypeptide) or may encode polypeptides having altered amino acid sequence. The term allelic variant is also used herein to denote a protein encoded by an allelic variant of a gene.
Zcyto7 and a method for making Zcyto7 polypeptides have been disclosed in International Patent Application No. PCT/US98/08212, Publication No. WO 98/49310.
Introduction
The present invention is based upon the discovery that Zcyto7 or IL-17 can induce the production of myelin by Schwann cells. The present invention is also based upon the discovery that Zcyto7 can induce the production of protein zero by Schwann Cells. Protein zero is a major structural protein of peripheral myelin, and is a homophilic immunoglobulin cell adhesion molecule, which mediates adhesion of Schwann cell membranes as they enwrap axons and generate compact myelin, Spiryda L. B., J. Neurosci, Res. 54: 137-146 (1998).
The axons of many vertebrate neurons are insulated by a myelin sheath, which greatly increases the rate at which an axon can conduct an action potential. Schwann cells, which are supporting or glial cells, form myelin in the peripheral nerves. The Schwann cells wrap layer upon layer of their own plasma membrane in a tight spiral around the axon, thereby insulating the axonal membrane so that almost no current leaks across it. The sheath is interrupted at regularly spaced intervals called the xe2x80x98nodes of Ranvierxe2x80x99, where almost all the Na+ channels in the axon are concentrated. Because the ensheathed portions of the axon membrane are so well insulated, a depolarization of the membrane at one node almost immediately spreads passively to the next node. Thus, an action potential propagates along a myelinated axon by jumping from node to node, a process called salutatory conduction. This type of conduction has two main advantages: action potentials travel faster, and metabolic energy is conserved because the active excitation is confined to the small regions of axonal plasma membrane at nodes of Ranvier. Conduction in myelinated axons is characterized by a rapid electronic conduction (because of the decreased time constant for conduction) with little decrement (because of the increased length constant) between the nodes of Ranvier. Only at the nodes is the action potential regenerated. A myelination of an axon increases electronic conduction velocity by sevenfold.
Myelinated axons are also more efficient metabolically than nonmyelinated axons. The sodium-potassium pump extrudes the sodium that enters and re-accumulates the potassium that leaves the cell during action potentials. In a myelinated axon, ionic currents are restricted to the small fraction of the membrane surface at the nodes of Ranvier. For this reason fewer Na+ and K+ ions traverse a unit area of membrane, and less ion pumping is required to maintain Na+ and K+ gradients.
The present invention is a method for inducing the expression of myelin or Protein zero by Schwann cells. Thus, Zcyto7 can be administered to treat a number of demyelinating PNS neuropathies, or to induce the production of myelin around regenerating peripheral nerve cells that have been injured by trauma.
Those skilled in the art will recognize that the sequences disclosed in SEQ ID NOS: 1, and 2 represent a single allele of the human Zcyto7. One can clone allelic variants of these sequences by probing cDNA or genomic libraries from different individuals according to standard procedures.
Acute Demyelinating Polyneuropathy
An example of a demyelinating disease of the PNS is acute demyelinating polyneuropathy. This acute inflammatory polyneuropathy, also known as Guillain-Barrxc3xa9 syndrome (GBS), occurs in all parts of the world and in all seasons. It affects children and adults of all ages and both sexes. A mild respiratory or gastrointestinal infection precedes the neuritic symptoms by 1 to 3 weeks in about 60 percent of the patients. Other less common antecedent events include surgical procedures, viral exanthems and other viral illnesses such as cytomegalovirus, Epstein-Barr virus, human immunodeficiency virus (HIV), bacterial infections, e.g., Mycoplasma pneumoniae, Lyme disease and particularly Campylobacter jejuni, and lymphoma, particularly Hodgkin""s disease.
Symptomatology
The major clinical manifestation of GBS is weakness, which evolves, more or less symmetrically, over a period of several days or a week or two. Proximal as well as distal muscles of the limbs are involved, usually the lower extremities before the upper trunk, intercostals, neck, and cranial muscles are affected later. The weakness can progress to total motor paralysis with death from respiratory failure within a few days. More than half of the patients complain of pain and an aching discomfort in the muscles, mainly those of the hips, thighs, and back. Paresthesias (tingling, burning, numbness) are also a frequent and early symptom but tend to be evanescent; occasionally they are absent throughout the illness. The most important laboratory aids are the cerebrospinal fluid (CSF) examination and electrodiagnostic studies. An increase in CSF protein is probably due to widespread inflammatory disease of the nerve roots. In a few patients (10 percent or less), the CSF protein values are normal throughout the illness.
Electrodiagnostic studies may be normal early in the illness. Then there occurs a reduction in conduction velocity or conduction block in motor neurons. Prolonged distal latencies and abnormal F responses (with affection of proximal parts of nerves) are other diagnostic findings.
Treatment
Most of the evidence suggests that the clinical manifestations of this disorder are the result of a cell-mediated immunologic reaction directed at peripheral nerves. In general administration of Zcyto7 should begin upon diagnosis of the disease at the dosages listed below. However, treatment with Zcyto7 may be delayed until the underlying inflammatory condition has subsided. Plasma exchange or intravenous administration of immunoglobulin can be employed to alleviate the inflammatory condition. For best results this should be done within two weeks of onset of symptoms. The usual plasma exchange regimen removes 200 to 250 mL/kg in four to six treatments on alternate days. The usual replacement fluid is saline and 5 percent albumin. Alternatively immunoglobulin can be administered at 0.4 g/kg/day for 5 consecutive days. Zcyto7 can be administered at the onset of the disease, during treatment to alleviate the inflammatory process or after the treatment. Administration of Zcyto7 should be continued on a regular basis, at least 1-3 times a week until full neurologic recovery by the patient.
In chronic inflammatory demyelinating polyradiculoneuropathy, other immunosuppressants and plasmapheresis can be used to alleviate the inflammatory condition and Zcyto7 can be administered to promote remyelination.
Diabetic Neuropathies
Zcyto7 can also be used to promote myelination expression in Schwann cells to treat diabetic neuropathies. The demyelination that occurs in diabetes mellitus is believed to be caused by ischemia. The patient should be administered Zcyto7 1 to 3 times a week at the dosages listed below.
Use of Zcyto7 to Promote Re-myelination of Peripheral Neurons Injured by Trauma
Unlike the central nervous system the neurons of the PNS have the ability to regenerate or repair themselves after injury caused by trauma. After an axon of the PNS is lost through trauma, the proximal stump of the damaged axon develops sprouts. In the PNS these sprouts elongate and grow along the path of the original nerve if this route is available. The Schwann cells in the distal stumps of the nerve not only survive the degeneration of the neuron, but they also proliferate and form rows along the course previously taken by the axons. Growth cones of the sprouting axons find their way along the rows of Schwann cells and may eventually reinnervate the original peripheral target structures. The Schwann cells then remyelinate the axons. To expedite the generation of the myelin sheath around the newly formed axon, Zcyto7 can be administered, preferably every one to three days until it becomes apparent the nerve is regenerated by means of the appropriate neurological test.
Modes of Administration
For pharmaceutical use, the proteins of the present invention are formulated for parenteral, particularly intravenous or subcutaneous, delivery according to conventional methods. Intravenous administration will be by bolus injection or infusion over a typical period of one to several hours. In general, pharmaceutical formulations will include a Zcyto7 protein in combination with a pharmaceutically acceptable vehicle, such as saline, buffered saline, 5% dextrose in water or the like. Formulations may further include one or more excipients, preservatives, solubilizers, buffering agents, albumin to prevent protein loss on vial surfaces, etc. Methods of formulation are well known in the art and are disclosed, for example, in Remington: The Science and Practice of Pharmacy, Gennaro, ed., (Mack Publishing Co., Easton, Pa., 19th ed., 1995). Therapeutic doses will generally be in the range of 0.1 to 100 xcexcg/kg of patient weight per day, preferably 0.5-20 xcexcg/kg per day, with the exact dose determined by the clinician according to accepted standards determination of dose is within the level of ordinary skill in the art. The proteins may be administered for acute treatment, over one week or less, often over a period of one to three days or may be used in chronic treatment, over several months or years.
Nucleic Acid-based Therapeutic Treatment
Zcyto7 can be also administered by means of gene therapy. In one embodiment, a gene encoding a Zcyto7 polypeptide is introduced in vivo in a viral vector. Such vectors include an attenuated or defective DNA virus, such as but not limited to herpes simplex virus (HSV), papillomavirus, Epstein Barr virus (EBV), adenovirus, adeno-associated virus (AAV), and the like. Defective viruses, which entirely or almost entirely lack viral genes, are preferred. A defective virus is not infective after introduction into a cell. Use of defective viral vectors allows for administration to cells in a specific, localized area, without concern that the vector can infect other cells. Examples of particular vectors include, but are not limited to, a defective herpes virus 1 (HSV1) vector [Kaplitt et al., Molec. Cell. Neurosci.2: 320-330 (1991)], an attenuated adenovirus vector, such as the vector described by Stratford-Perricaudet et al., J. Clin. Invest. 90 :626-630 (1992), and a defective adeno-associated virus vector [Samulski et al., J. Virol., 61:3096-3101 (1987); Samulski et al. J. Virol., 63:3822-3828 (1989)].
In another embodiment, the gene can be introduced in a retroviral vector, e.g., as described in Anderson et al., U.S. Pat. No. 5,399,346; Mann et al., Cell, 33:153 (1983); Temin et al., U.S. Pat. No. 4,650,764; Temin et al., U.S. Pat. No. 4,980,289; Markowitz et al., J. Virol. 62:1120 (1988); Temin et al., U.S. Pat. No. 5,124,263; International Patent Publication No. WO 95/07358, published Mar. 16, 1995 by Dougherty et al. and Blood, 82:845 (1993).
Alternatively, the vector can be introduced by lipofection in vivo using liposomes. Synthetic cationic lipids can be used to prepare liposomes for in vivo transfection of a gene encoding a marker [Felgner et al., Proc. Natl. Acad. Sci. USA, 84:7413-7417 (1987); see Mackey et al., Proc. Natl. Acad. Sci. USA, 85:8027-8031 (1988)]. The use of lipofection to introduce exogenous genes into specific organs in vivo has certain practical advantages. Molecular targeting of liposomes to specific cells represents one area of benefit. It is clear that directing transfection to particular cells represents one area of benefit. It is clear that directing transfection to particular cell types would be particularly advantageous in a tissue with cellular heterogeneity, such as the pancreas, liver, kidney, and brain. Lipids may be chemically coupled to other molecules for the purpose of targeting. Targeted peptides, e.g., hormones or neurotransmitters, and proteins such as antibodies, or non-peptide molecules could be coupled to liposomes chemically.
It is possible to remove the cells from the body and introduce the vector as a naked DNA plasmid and then re-implant the transformed cells into the body. Naked DNA vector for gene therapy can be introduced into the desired host cells by methods known in the art, e.g., transfection, electroporation, microinjection, transduction, cell fusion, DEAE dextran, calcium phosphate precipitation, use of a gene gun or use of a DNA vector transporter [see, e.g., Wu et al., J. Biol. Chem., 267:963-967 (1992); Wu et al., J. Biol. Chem., 263:14621-14624 (1988)].